A typical thyristor of the above type is the MOS-controlled thyristor (MCT) described in a paper by V. A. K. Temple et al appearing in the November 1992 issue of Power Conversion Intelligent Motion, pp. 9-16. Another example of such a thyristor is disclosed and claimed in U.S. patent application Ser. No. 08/381,766--Piccone et al, filed on Feb. 1, 1995, and assigned to the assignee of the present invention. Each of these thyristors comprises a multi-layer semiconductor body having four layers, with contiguous layers being of different P and N conductivity types, with each end layer constituting an emitter layer and the two intermediate layers constituting base layers, the upper base layer serving also as a gate layer. The upper emitter layer is of an arrayed cellular construction. When the thyristor is in its "on" state, current flows in series through these four layers, passing in parallel paths through the cells of the upper emitter layer. Turn-off of this thyristor is effected by relying upon field-effect transistors that are respectively integrated into all the cells of the upper emitter layer. These field-effect transistors are non-conducting when the thyristor is in its "on" state, but each is switchable into a conducting state that results in the field-effect transistor effectively bypassing its associated upper base-upper emitter PN junction, thereby turning off the thyristor.
In each of the above-described thyristors, each cell of the thyristor includes a field-effect transistor integrated into the cell, with certain components of the cell serving also as some of the components of the field-effect transistor. One disadvantage of this type of construction is that manufacture of the field-effect transistors must be performed by integrated-circuit fabricating procedures, and because the transistors are integrated into the cells of the thyristor, the whole thyristor is required to be fabricated by such procedures. Integrated-circuit fabricating procedures are much more demanding from precision and cleanliness standpoints than are the procedures normally used for fabricating high-power thyristors. Hence, fabricating the above-described prior MOS-controlled thyristors becomes a very expensive proposition as compared to fabricating more conventional comparably-rated high-power thyristors.